Data may be transmitted between different devices in a communication system through a “data link”. The component that generates and transmits a signal through the data link may be referred to as a “transmitter”; whereas, the component that receives the signal over the data link and extracts information from the signal may be referred to as a “receiver.” In communications, modulation is the process of varying a periodic waveform in order to use that signal to convey a message. The electronic waveform is the key to transmitting information in both analog and digital communications networks. Amplitude modulation (AM) is a technique used in electronic communications, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength/amplitude of the transmitted signal in relation to the information being sent. Frequency modulation (FM) conveys information over a carrier wave by varying its frequency.
Digital communications use a rapidly changing voltage waveform to signify the stream of ones and zeros that make up the transfer of digital information. The voltage is measured at various time intervals to to determine if a data bit is a “1” or a “0”. Distortion of the waveform can prevent the data bit from being properly interpreted and cause an error that must be corrected through error checking and retransmission of information. Ringing and distortion of the waveform signal can be caused by capacitance and inductance due to cabling length, properties of the cable, the number and configuration of cabling runs, and electromagnetic interference (EMI) from other sources.
Traditional digital communications use an electrical signal of varying voltage with a certain frequency (the carrier frequency) to transmit information. Certain features of the waveform will determine if the segment of the waveform is transmitting data meant to be interpreted as a “1” or a “0”. The integrity of a digital network is based on how closely the waveform adheres to the criteria and tolerances required to interpret the zeros and ones based on the rapidly changing voltage levels.
The waveform may be amplitude or frequency modulated to transmit the information, but the base frequency and ideal waveform shape are typically constant for the 1's and 0's that flow on the communications bus. Many of these communications networks use a packet transfer methodology, where packets of data are error checked and re-transmitted if there is any corruption detected. The problem with this technique is that if the waveform is badly corrupted then a packet may not be capable of transmission at all, or it could require a great number of transmissions of a packet before it is received in an uncorrupted state.
Waveform corruption can be caused by capacitive and inductive effects of the cable itself, as well as electromagnetic interference (EMI) caused by nearly electronics, power cables, or other equipment that can produce EMI.
The current state of the art deals with the problem of waveform corruption by placing limits on the cable lengths thus controlling the amount of capacitance and inductance in the cable and keeping the waveform within a certain specified shape.
A number of digital network quality control systems exist such as those described in U.S. Pat. Nos. 5,107,520, 6,990,294, 6,134,589, 7,406,052, 7,502,594, 20090076751, all of which are incorporated herein by reference.